Typical examples of charge accumulating type chemical and physical phenomenon detecting apparatuses are disclosed in patent document 1 and patent document 2.
FIG. 1 shows an example of using a charge accumulating type chemical and physical phenomenon detecting apparatus for measuring ion concentration.
On a silicon substrate 10, n+ type dope regions 11, 13, and a p type dope region 15 are formed. In the p type dope region 15, a silicon oxide film 19 is deposited as a gate insulation film. On this silicon oxide film 19, two gate electrodes 22 and 24 are provided. Reference numeral 23 in the drawing is a silicon nitride film. On the silicon nitride film 23, a liquid cell 31 is provided, which is filled with an aqueous solution 32 for measuring the ion concentration (pH). Reference numeral 26 is a reference electrode, which is kept at a specific potential.
Those provided in the substrate, that is, the n+ region 11, the gate electrode 22, the gate electrode 24, and the n+ region 13 are respectively connected to terminals ID, ICG, TG, and FD, and a specific potential is applied at a specific timing. As a result, the n+ region 11 of the substrate becomes a charge supply unit 1, the portion corresponding to the gate electrode 22 becomes a charge injection adjusting part 2, the portion corresponding to the silicon nitride film 23 becomes a sensing part 3, the portion corresponding to the gate electrode 24 becomes a barrier part 4, and the n+ type region 13 becomes a floating diffusion part 5.
In the charge accumulating type chemical and physical phenomenon detecting apparatus of the prior art having such configuration, a theoretical operation is shown in FIG. 2.
In standby state S1, an electric charge is accumulated in a floating diffusion part 5. This charge is accumulated by unit detection operation up to the last time. At this time, corresponding to the ion concentration of a solution 32, the potential of a sensing part 3 is changed.
By lowering the potential to be applied to a charge supply unit 1, an electric charge is supplied in the sensing part 3 (step 3). Consequently, by raising the potential of the charge supply unit 1, the charge scooped by a charge injection adjusting part 2 is left over in the sensing part 3 (step 5). At step 7, this residual charge is accumulated in the floating diffusion part 5.
By repeating the unit detection operations at step 1 to step 7, the charge is accumulated in the floating diffusion part 5. As a result, the sensitivity of detection is enhanced as shown in FIG. 3.    Patent document 1: Japanese Patent Application Laid-Open (JP-A) No. 10-332423    Patent document 2: JP-A No. 2002-98667